Well Jarod's been building a CNC machine, I've been watching, learning, and trying to solve some of the problems he's run into before starting mine. I've finally begun construction. Linear bearings were my big hangup, I wanted the perfect solution, but it has eluded me. I decided to try the angle iron / 608zz bearing based system I've seen on the internet. I don't think it's perfect, but it's the best system I've seen so far. Anyway, enough talk, lets see some pics!

Linear Bearings

End View

I Built the X-axis to test the design. I welded 1 1/2 angle to the ends of the rails and in the center of each carriage to attach the parts.

X-Axis

Under side of X-axis

I'm not sure how bad the deflection will be, but it will certainly support some weight. I may need some way to tension it or some other way to to control the deflection once I get the table on it.

With one foot and most of my weight it has a bit more friction than unloaded, but still very little. I'm not quite sure how to describe it, I would say it's kind of like walking on wet ice, but different. I haven't worn roller skates in years, maybe like that, only with 6" of travel forward & back.
I didn't move it with both feet it, It felt really unstable, like if it started to move it would go all the way to the stop and I'd come crashing down. It may have just been my imagination. I kept thinking "this is a bad idea, bad idea, bad idea..."

Bought more angle iron today, so I should be resuming my build shortly. I also bought some 1/2" steel conduit for another project and noticed it was about the right size to sit between the bearings. I tried it an it fits perfectly, and seems quite rigid (not as strong as the angle) so now I'm not sure whether to cut up the angle iron or build a test axis out of conduit. The angle costs about $1.10/ft and the conduit about $0.25/ft, if it would work it would be a huge cost savings. It would also save time as it doesn't need to be at a precise angle to align with the bearings. I doubt I could stand on it, but that's really overkill (not that there's anything wrong with that). I'm thinking a quick test axis would be a good idea, though I hate to change away from a tested design and waste time at this point.

The steel conduit is definitely weaker, as expected. I think it could work ok though. I could just stand on it, if I bounced on it slightly the carriage dropped through. I Proceed with angle iron, should have had enough, but goofed and made 2 16" slides that should have been 18". So I'm out again. I did get the Y-axis built.

How wide is your frame? if it's 16" I happen to have a set of rails. My x axis uses 16" rails, my y axis uses 18" rails, the Z axis will use 12". Subtract 4" for approx max travel. I need to weld up some carriages for you, I'm out of 1" angle again and I've broken my good drill bit. I have another the same size ,but It's so dull it might be quicker to drive it through with a hammer.

I've got partial carriages for you, I need to add the angle to the back of them. You should just need rails, they are much easier to build than the carriages.

I will probably end up redoing these because of the angle of the motor interfering with axis travel and mounting issues. I'll end up having the motors square with the bracket instead of at a 45 degree angle.